It has long been recognized that it is important in lighting fixtures that employ the above type of quartz-halogen lamp that the longitudinal axis of the lamp envelope be disposed substantially horizontally. Such horizontal disposition is needed in order to achieve a long life and good lumen maintenance from the lamp, partially because of thermal considerations and partially because of the role of the horizontal disposition in assuring correct operation of the halogen cycle.
One of the major applications for quartz-halogen lamps is in small floodlights, which typically use a trough-like, horizontally-oriented reflector, with the lamp suitably placed in the trough for the desired light distribution. The floodlight is generally equipped with a support stem having external threads on its open end for threaded engagement with an internally-threaded hole in suitable support structure, e.g., a conduit fitting on the side of a building or a pole-mounted bracket. In the usual mounting arrangement, the support stem extends horizontally.
In residential lighting applications, the typical mounting arrangement for the floodlight includes the above-described horizontally-extending, externally-threaded support stem and a cast cover for the typical wiring box used on houses or garages. The horizontally-extending support stem is threaded into an internally-threaded hole in the cast cover. The floodlight is usually equipped with a pivot joint, or knuckle, for adjustably supporting the floodlight housing on the support stem. This knuckle typically allows the floodlight housing to be adjusted for vertical movement, i.e., pivotal motion about a horizontal axis so as to provide for vertical adjustments of its light-aiming angle. But there is no provision in such mounting arrangements for adjustment about a vertical axis, i.e., horizontal adjustments of the light-aiming angle. While it is possible to make certain adjustments in orientation of the floodlight by further screwing the support stem into the cast cover by a partial turn and then locking it in place, this is not an acceptable way of adjusting a quartz-halogen type of floodlight because it causes the quartz-halogen lamp within the floodlight to be tilted out of its required horizontal disposition.